This can happen if ifi fails to be read from the netlink message and the
error is ENODATA.
Fixes the following valgrind message when running netstat:
==164141== Conditional jump or move depends on uninitialised value(s)
==164141== at 0x524AE60: address_compare (local-addresses.c:29)
==164141== by 0x48BCC78: msort_with_tmp.part.0 (msort.c:105)
==164141== by 0x48BC9E4: msort_with_tmp (msort.c:45)
==164141== by 0x48BC9E4: msort_with_tmp.part.0 (msort.c:53)
==164141== by 0x48BCF85: msort_with_tmp (msort.c:45)
==164141== by 0x48BCF85: qsort_r (msort.c:297)
==164141== by 0x52500FC: UnknownInlinedFun (sort-util.h:47)
==164141== by 0x52500FC: local_gateways.constprop.0 (local-addresses.c:310)
==164141== by 0x5251C05: _nss_myhostname_gethostbyaddr2_r (nss-myhostname.c:456)
==164141== by 0x5252006: _nss_myhostname_gethostbyaddr_r (nss-myhostname.c:500)
==164141== by 0x498E7FE: gethostbyaddr_r@@GLIBC_2.2.5 (getXXbyYY_r.c:274)
==164141== by 0x498E560: gethostbyaddr (getXXbyYY.c:135)
==164141== by 0x121353: INET_rresolve.constprop.0 (inet.c:212)
==164141== by 0x1135B9: INET_sprint (inet.c:261)
==164141== by 0x121BFC: addr_do_one.constprop.0.isra.0 (netstat.c:1156)